Switched mode power converters, which may also be referred to as switched mode power supplies (SMPS), are widely used for converting power in different types of automotive, industrial, consumer electronic or household applications. A switched mode power converter includes at least one inductor, an electronic circuit connected in series with the at least one inductor, and a rectifier circuit coupled to the at least one inductor. The series circuit with the at least one inductor and the electronic switch is coupled to an input where the power converter receives an input power, and the rectifier circuit is coupled to an output where the power converter supplies an output power. The input power, which is an input voltage multiplied with an input current, and, therefore, the output power, which is an output voltage multiplied with an output current, can be controlled by controlling a current through the at least one inductor. Controlling the current through the at least one inductor may include operating the electronic switch in a pulse-width modulated (PWM) fashion.
In a power converter with peak current control a controller detects a current flowing through the at least one inductor and switches off the electronic switch each time the current reaches a predefined threshold. The controller may switch on the electronic switch at a fixed frequency; this can be referred to as fixed frequency control. Alternatively, the controller may switch on the electronic switch after a fixed delay time (off-time) after the electronic switch has been switched off; this can be referred to as fixed off-time control.
Due to parasitic effects oscillations of the current flowing through the inductor may occur in a short time period after switching on the electronic switch. Those oscillations may cause the current to rise above the threshold for a short time. In order to prevent the controller from switching off the electronic switch triggered by those oscillations the controller may employ a minimum on-time. That is, the electronic switch is switched on at least for the minimum on-time and the controller starts to monitor the current flowing through the inductor not before the end of the minimum on-time. This, however, may cause the input power of the power converter to be higher than required which, in turn, may cause the output voltage to increase.